This invention relates to core barrels, and more particularly to improvements in core barrel teeth and the installation thereof.
In the fabrication of drilled shafts, hard materials such as rock are often removed by means of core barrels. Such a device comprises a hollow cylinder of uniform diameter throughout its length. In some instances the upper and lower portions of the cylinder are formed from different materials, with the lower portion comprising a wear-resistant material. A series of cutting teeth are typically provided around the lower edge of the cylinder comprising the core barrel. Apparatus is provided at the upper end of the core barrel for attaching the device to a kelly which functions both to rotate the core barrel and to control its vertical positioning.
In the use of a core barrel, the kelly is actuated first to position the lower end of the core barrel and the cutting teeth thereon in engagement with the materials to be cored or cut, and then to rotate the core barrel. By this means there is formed a circular slot or kerf surrounding the material to be removed. As the formation of the circular kerf continues, the material to be removed advances into the interior of the core barrel in the form of a cylinder. Then, when a layer of relatively weak material is encountered, the cylinder of hard material shears away from the underlying structure and rotates with the core barrel under the action of the kelly. At this point the kelly may be actuated to remove the core barrel and the cylinder of hard materials contained therein from the drilled shaft that is being fabricated. Typically the fines and other small pieces of hard material which are present within the core barrel as a result of the cutting operation are sufficient to frictionally and mechanically retain the cylinder within the core barrel as it is removed from the drilled shaft.
One of the problems that has been involved in the use of the core barrels available heretofore relates to the construction and installation of core barrel teeth. Typically, two types of core barrel teeth have been provided. In accordance with one procedure core barrel teeth are built upon the lower end of the core barrel cylinder utilizing lengths of hard material which are secured to the core barrel cylinder by means of brazing or welding techniques. This has proven to be unsatisfactory because the teeth are difficult and time consuming to replace in the field.
In accordance with the other conventional technique for providing core barrel teeth, a plurality of tooth retaining pockets are welded to the lower end of the core barrel cylinder. A plurality of teeth are also provided, with each tooth comprising a metal body having a tip formed from carbide or other hard materials secured thereto and having an attachment lug extending from one end. The attachment lug is received in the tooth retaining pocket and is secured therein by means of a fastener. This technique has also proved to be inadequate under field conditions primarily due to breakage which can occur either at the point of connection of the tooth retaining pocket to the core barrel cylinder or at the point of connection of the retaining lug to the body.
Another problem that has been involved in the use of core barrels heretofore relates to the replacement of core barrel teeth when the drilled shaft is partially fabricated. As the core barrel teeth eventually become worn, the diameter of the circular kerf formed by the teeth is reduced. Upon replacing the core barrel teeth, the diameter of circular kerf described by the new, wider teeth exceeds that formed by the worn teeth. The result is a lateral shearing force exerted on the new teeth by the surrounding rock of the drilled shaft that can cause the new teeth to be broken or otherwise damaged.
The present invention relates to improvements in core barrel teeth and the installation thereof which overcome the foregoing and other problems long since associated with the prior art. In accordance with the broader aspects of the invention, a core barrel tooth comprises a central body portion having opposed lateral flanges extending from the rearward and forward direction and bifurcations extending from one end of the lateral flanges thereof which are spaced apart to receive the inner and outer surfaces of the cylinder of a core barrel. The lower end of the core barrel cylinder is in turn provided with a plurality of notches each having edges positioned to engage the forward and rearward end surfaces of the central body portion of the tooth body of one of the core barrel teeth, while the opposed lateral flanges engage the inner and outer surfaces of the cylinder adjacent the opposing edges of the notch and the bifurcations engage the inner and outer surfaces adjacent the other edge of the notch. In this manner there is formed between each core barrel tooth and the core barrel cylinder a connection which is very strong and rigid in the direction of both the applied rotational force and the lateral shearing force.
In accordance with more specific aspects of the invention, the bifurcations of each core barrel tooth are provided with aligned apertures, and a roll pin is received through these apertures and through an aperture formed in the adjacent portion of the cylinder of the core barrel to retain the tooth in engagement with the core barrel cylinder. In this manner the field replacement of worn core barrel teeth is facilitated. A tip formed from carbide or other hard material may be secured to the tooth body of each core barrel tooth by means of brazing or welding. The tip is preferably secured in a notch formed in the forward lateral flanges of the tooth body and has a generally rectangular shape which can extend to a pointed lower end. The end of the tooth body receiving the cutting tip is canted upwardly and rearwardly away from the forward edge of the cutting end receiving the cutting tip.